test-basic: make test compatible with chg

The error codes returned when writing to /dev/full are different after
the first failure with and without '--chg' option. Therefore, this commit
conditionally handles the error codes as appropriate.

Test Plan:
Ran the test 'test-basic.t' with and without '--chg' option.

Differential Revision: https://phab.mercurial-scm.org/D922

tests/test-basic.t

@@ -31,7 +31,9 b' Writes to stdio succeed and fail appropr'
   $ hg status >/dev/full
   abort: No space left on device
   [255]
+#endif
 
+#if devfull no-chg
   $ hg status >/dev/full 2>&1
   [1]
 
@@ -39,6 +41,14 b' Writes to stdio succeed and fail appropr'
   [1]
 #endif
 
+#if devfull chg
+  $ hg status >/dev/full 2>&1
+  [255]
+
+  $ hg status ENOENT 2>/dev/full
+  [255]
+#endif
+
   $ hg commit -m test
 
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